Conventional plasma-assisted coating processes normally involve igniting a plasma in a partial vacuum, for example, during magnetron or radio-frequency sputter deposition. In some instances, material-processing flexibility is limited because of the fixed shape and size of the sputter deposition chamber and the need to maintain a vacuum seal. When coating large parts, large containers have been required, but such containers can make it difficult to maintain a reliable vacuum, which can significantly increase costs and slow down the process speed. Thus, vacuum integrity and the object size can affect efficiency and throughput during a plasma-assisted coating process.
Another plasma-assisted coating method is plasma spray deposition. During this method, material is reportedly deposited on a surface by compounding a buildup of “splats” of molten material on the surface. The heat of the plasma either melts or vaporizes material injected into path of the plasma ejected from a nozzle, and the material impinges on the surface of a work piece at high velocity. Typical coatings that have been reported by this method are thermal barrier coatings and oxide coatings. However, when coating an object with raised or depressed surface features, or an object with a complex shape, such as a gear or fan blade, the object must be positioned and appropriately rotated in the path of the plasma spray produced by a focused nozzle. Also, plasma spray deposition typically requires expensive equipment and can only be used on a limited range of materials because of the relatively high heat and thermal shock inherent in this technique.